Despite tremendous efforts to prevent or cure ovarian cancer, its incidence and high mortality has remained largely unchanged. There are no proven methods of early prevention, and chemotherapeutic agents often are highly cytotoxic and cause severe side effects. We have generated new mouse ovarian surface epithelial (MOSE) cell lines that mimic early stages of ovarian cancer that progress to intermediate and late stages. Aberrant gene methylation accompanies the progression of these cells that can be prevented by sphingosine. Our long-term goal is to understand the regulation of transformed cells by non-toxic doses of sphingolipids, and apply this knowledge to cancer prevention and treatment with orally administered sphingolipids Here we propose to investigate the central hypothesis is that non-toxic doses of sphingosine prevent aberrant DNA methylation of tumor suppressor genes, activate their re-expression and, thereby, prevent or suppress ovarian tumor progression and metastasis. This hypothesis has been formulated based on our preliminary studies that show that sphingosine prevents and/or reverses epigenetic silencing of E-cadherin and lowers the tumorigenic potential of the MOSE cells in vitro. This hypothesis will be tested by pursuing the following specific aims: 1) To determine the mechanisms of how non-toxic doses of sphingosine regulate gene methylation. 2) To determine sphingosine-mediated changes in epigenetic silening that accompanies progression of MOSE cells. 3) To determine to what extent the regulation of epigenetic silencing is associated with the prevention of tumor formation and metastasis by dietary sphingomyelin in a syngeneic model. The proposed research is highly significant because the reversal of epigenetic silencing of tumor suppressors that occurs early in carcinogenesis is a critical step in the prevention of cancer. The proposed studies will provide the mechanistic basis for the development of a chemopreventive and possibly chemotherapeutic strategy using orally administered complex sphingolipids. The proposed studies will also greatly enhance our knowledge on the mechanisms of how long-term exposure to non-toxic concentrations of sphingosine reverses aberrant protein expression in cancer cells.